Ink, method of manufacturing ink, and ink cartridge

ABSTRACT

In the Chemical formula, R represents a hydrogen atom or a methyl group, X represents an alkylene group having 2-4 carbon atoms, and Y represents a substituted or non-substituted straight-chain alkylene group having 5 to 7 carbon atoms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. § 119 to Japanese Patent Application No. 2015-211691, filed onOct. 28, 2015, in the Japan Patent Office, the entire disclosure ofwhich is hereby incorporated by reference herein.

BACKGROUND

Technical Field

The present invention relates to ink, a method of manufacturing ink, andan ink cartridge.

Description of the Related Art

Inkjet recording methods have advantages such that the process is simpleand full colorization is easy in comparison with other recordingmethods. Therefore, high resolution images can be obtained by a devicehaving a simple configuration. For this reason, inkjet recording iswidely diffusing from home use to office use, commercial printing, andindustrial printing. However, aqueous ink using a water-soluble dye asthe coloring material used in inkjet recording methods is inferior withregard to water resistance and light resistance. Therefore, pigment inkusing a water insoluble pigment is under development.

For inkjet ink printing for office use, recording media, typically plainpaper, are used and high image density is demanded. In general, whenimages are printed on plain paper using pigment ink, the pigment inkdoes not stay on the surface of the paper but permeates into the paper,so that the density of the pigment on the surface decreases andconsequently the image density lowers. Image density increases ifconcentration of pigments in the ink is increased. However, the inkbecomes viscous, thereby degrading the discharging stability of the ink.

Moreover, water contained in the pigment ink swells the surface of plainpaper immediately after the ink droplets land on the paper. As a result,the extension percentage differs between the top surface and the bottomsurface of the paper, which causes the paper to curl. This phenomenondoes not cause a problem during low performance. However, as theprinting speed increases, recording media are transferred (conveyed)before curling is canceled after printing, which naturally leads tooccurrence of paper jam. To prevent this paper jam, it is suitable toadd a permeating agent to a pigment ink to promote water to permeateinto paper. However, ink becomes hydrophobic by the agent, which makesit difficult to secure storage stability of the ink. Also, the pigmentink more easily permeates into a recording medium, thereby furthermoredecreasing image density.

SUMMARY

According to the present invention, provided is an improved ink whichincludes water, a coloring material, and a copolymer including a firststructure unit represented by the following Chemical formula 1 and asecond structure unit including an anionic group.

In the Chemical formula, R represents a hydrogen atom or a methyl group,X represents an alkylene group having 2-4 carbon atoms, and Y representsa substituted or non-substituted straight-chain alkylene group having5-7 carbon atoms.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Various other objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the detailed description when considered in connectionwith the accompanying drawings in which like reference charactersdesignate like corresponding parts throughout and wherein:

FIG. 1 is a schematic diagram illustrating an example of an inkcartridge according to an embodiment of the present disclosure; and

FIG. 2 is a diagram illustrating the ink cartridge illustrated in FIG. 1including its housing.

The accompanying drawings are intended to depict example embodiments ofthe present invention and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted. Also, identical or similar referencenumerals designate identical or similar components throughout theseveral views.

DESCRIPTION OF THE EMBODIMENTS

In describing embodiments illustrated in the drawings, specificterminology is employed for the sake of clarity. However, the disclosureof this specification is not intended to be limited to the specificterminology so selected and it is to be understood that each specificelement includes all technical equivalents that have a similar function,operate in a similar manner, and achieve a similar result.

As used herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

Embodiment 1 of the present disclosure is ink which includes water, acoloring material, and a copolymer including a first structure unitrepresented by the following Chemical formula 1 and a second structureunit including an anionic group.

In Chemical formula 1, R represents a hydrogen atom or a methyl group, Xrepresents an alkylene group having 2-4 carbon atoms, and Y represents asubstituted or non-substituted straight-chain alkylene group having 5-7carbon atoms.

Embodiment 1 as one aspect of the present disclosure is described indetail. Since the following embodiments 2-6 are included in the presentdisclosure, these are also described.

2. The ink according to 1 mentioned above, wherein the second structureunit includes a carboxylic group.

3. The ink according to 1 or 2 mentioned above, wherein the proportionof the first structure unit in the copolymer is 75-90 percent by mass.

4. The ink according to any one of 1-3, wherein the mass averagemolecular weight of the copolymer is 15,000-40,000.

5. A method of manufacturing ink including water, a coloring material,and a copolymer, including synthesizing the copolymer by radicalpolymerization of a monomer mixture including a monomer represented bythe following Chemical formula 2 and a monomer including an anionicgroup and mixing the copolymer, the coloring material and the water.

In the Chemical formula 2, R represents a hydrogen atom or a methylgroup, X represents an alkylene group having 2-4 carbon atoms and Yrepresents a substituted or non-substituted alkylene group having 5-7carbon atoms.

6. An ink cartridge including the ink of any one of 1-4 and a containerto accommodate the ink of any one of 1-4.

Copolymer

The copolymer for use in the present disclosure includes the firststructure unit represented by the following Chemical formula 1 and thesecond structure unit including an anionic group.

Structure Units Represented by Chemical Formula 1

In the Chemical formula 1, Y represents a substituted or non-substitutedstraight-chain alkylene group having 5-7 carbon atoms. Specific examplesof the substituents include, but are not limited to, methyl group,methoxy carbonyl group, halogen, and a functional group having halogen.

Specific examples of the structure unit represented by the Chemicalformula 1 are illustrated below but are not limited thereto.

The naphtyl group present at the distal end via Y has an excellentpigment adsorption power due to π-π stacking with pigments serving asthe coloring material in the ink. When a pigment dispersion in which apigment is dispersed in water is prepared using the copolymer mentionedabove, adsorption power with the pigment is strong. As a result,dispersion stability is enhanced and the thus-obtained dispersion hasgood storage stability. Moreover, when a hydrophilic organic solvent isadded to ink, dispersibility is maintained so that the obtaineddispersion has good storage stability.

In addition, when the copolymer mentioned above is used for ink, thedensity of images recorded on plain paper becomes high. This mechanismis not clear but can be inferred as follows.

In ink using the copolymer mentioned above, pigments have gooddispersion stability so that coarse particles are not easily formed whenthe ink is attached to the surface of plain paper. If coarse particlesare formed, exposed portions where no pigment is attached to the surfaceof plain paper tend to appear. As a result, image density lowers. To thecontrary, ink using the copolymer mentioned above can uniformly coverthe surface of plain paper so that high image density is obtained.

Structure Units Having Anionic Group

The structure unit having an anionic group is formed by copolymerizationof monomers having anionic groups. Examples of the monomer having ananionic group are unsaturated carboxylic acid monomers, unsaturatedsulfonic acid monomers, and unsaturated phosphoric acid monomers.

Specific examples of the unsaturated carboxylic acid monomers include,but are not limited to, acrylic acid, methacrylic acid, itaconic acid,fumaric acid, and maleic acid.

Specific examples of unsaturated sulfonic acid monomers include, but arenot limited to, styrene sulfonic acid, 2-acrylamide-2-methyl propanesulfonic acid.

Specific examples of unsaturated phosphoric acid monomers include, butare not limited to, vinyl phosphoric acid, vinyl phosphate,bis(methcryloxyethyl)phosphate, diphenyl-2-acryloyloxy ethylphosphate,disphenyl-2-methacryloyloxy ethylphosphate, and dibutyl-2-acryloyloxyethylphosphate.

Of these, monomers having carboxyl groups are preferable and avrylicacid and methacrylic acid are more preferable,

Examples of the structure unit having an anionic group are as followsbut are not limited thereto.

The monomer having an anionic group can be used alone or in combination.The structure unit having an anionic group may be neutralized by a base.

Specific examples of the base include, but are not limited to, sodiumhydroxide, potassium hydroxide, lithium hydroxide, tetramethyl ammoniumhydroxide, tetraethyl ammonium hydroxide, tetrapropyl ammoniumhydroxide, tetrabutyl ammonium hydroxide, tetrapentyl ammoniumhydroxide, tetrahexyl ammonium hydroxide, triethylmethyl ammoniumhydroxide, tributylmethyl ammonium hydroxide, trioctylmethyl ammoniumhydroxide, 2-hydroxyethyl trimethyl ammonium hydroxide,tris(2-hydroxyethyl)methyl ammonium hydroxide, propyltrimethyl ammoniumhydroxide, hexyltrimethyl ammonium hydroxide, octyltrimethyl ammoniumhydroxide, nonyltrimethyl ammonium hydroxide, decyltrimethyl ammoniumhydroxide, dodecyltrimerthyl ammonium hydroxide, tetradecyltrimethylammonium hydroxide, hexadecyl trimethyl ammonium hydroxide, octadecyltrimethyl ammonium hydroxide, didodecyl dimethyl ammonium hydroxide,ditetradecyl dimethyl ammonium hydroxide, dihexyadecyl dimethyl ammoniumhydroxide, dioctadecyl dimethyl ammonium hydroxide, ethylhexadecyldimethyl ammonium hydroxide, ammonium water, dimethyl amine, trimethylamine, monoethyl amine, diethyl amine, triethyl amine, monoethanolamine, diethanol amine, triethanol amine, methyl ethanol amine,methyldiethanol amine, dimethylethanol amine, monopropanol amine,dipropanol amine, tripropanol amine, isopropanol amine, morpholine,N-methyl morpholine, N-methyl-2-pyrolidone, and 2-pyrolidone.

These bases serving as neutralizing agents can be used alone or incombination.

Neutralizing treatment can be conducted when the monomer having ananionic group is co-polymerized or when dissolving the copolymer.

Composition Ratio

The proportion of the structure unit represented by the Chemical formula1 is not particularly limited and can be suitably determined to suit toa particular application. The proportion is preferably 60-90 percent andmore preferably 75-90 percent by mass to the total amount of thecopolymer mentioned above. When the proportion is within this range, ahigh image density and good storage stability are obtained when used forink, which is advantageous.

Molecular Weight

The mass average molecular weight of the copolymer is preferably5,000-50,000 and more preferably 15,000-40,000 in polystyreneconversion. When the mass average molecular weight is within this range,a high image density and good storage stability are obtained when usedfor ink, which is advantageous.

Other Monomers

The copolymer mentioned above may furthermore optionally include astructure unit formed of other polymerizable monomers in addition to thestructure unit represented by the Chemical formula 1 and the structureunit having an anionic group.

Such other polymerizable monomers are not particularly limited. Thesecan be selected to suit to a particular application. Examples thereofare polymerizable hydrophobic monomers, polymerizable hydrophilicmonomers, and polymerizable surfactants.

Specific examples of the polymerizable hydrophobic monomer include, butare not limited to, unsaturated ethylene monomers having aromatic ringsuch as styrene, α-methyl styrene, 4-t-butyl styrene, and 4-chloromethylstyrene; (meth)acrlic acid alkyl such as methyl (meth)acrylate,ethyl(meth)acrylate, (meth)acrylic acid-n-butyl, dimethyl maleate,dimethyl itaconate, dimethyl fumarate, lauryl(meth)acrylate (C12),tridecyl(meth)acrylate (C13), tetradecyl(meth)acrylate (C14),pentadecyl(meth)acrylate (C15), hexadecyl(meth)acrylate (C16),heptadecyl(meth)acrylate (C17), nonadecyl(meth)acrylate (C19),eicosyl(meth)acrylate (C20), heneicosyl(meth)acrylate (C21), anddocosyl(meth)acrylate (C22); and unsaturated ethylene monomers having analkyl group such as 1-heptene, 3,3-dimethyl-1-pentene,4,4-dimethyl-1-pentene, 3-methyl-1-hexene, 4-methyl-1-hexene,5-methyl-1-hexene, 1-octene, 3,3-dimethyl-1-hexene,3,4-diemthyl-1-hexene, 4,4-diemthyl-1-hexene, 1-nonene,3,5,5-trimethyl-1-hexene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene,1-tetracene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene,1-nonadecene, 1-eicocene, and 1-dococene. These can be used alone or incombination.

Specific examples of the polymerizable hydrophilic monomers include, butare not limited to, nonionic unsaturated ethylene monomers such as(meth)acrylic acid-2-hydroxyethyl, diethylene glycol mono(meth)acrylate,triethylene glycol mono(meth)acrylate, tetraethylene glycolmono(meth)acrylate, polyethylene glycol mono(meth)acrylate,(meth)acrylamide, N-methylol(meth)acrylamide, N-vinyl formamide,N-vinylacetoamide, N-vinylpyrolidone, acrylamide, N,N-dimethylacrylamide, N-t-butyl acrylamide, N-octyl acrylamide, and N-t-octylacrylamide.

One or more kinds of the polymerizable hydrophilic monomers andpolymerizable hydrophobic monomers are mixed and the proportion of themixture is 5-100 percent by mass of the total of the monomer forming thestructure unit represented by the Chemical formula 1 and the monomerforming the structure unit having an anionic group.

Synthesis of Copolymer

The copolymer can be obtained by co-polymerizing the monomer representedby the Chemical formula 2 and the monomer having an anionic group underthe presence of a radical polymerization initiator.

In the Chemical formula 2, Y represents a substituted or non-substitutedstraight-chain alkylene group having 5-7 carbon atoms.

Specific examples of the substituents include, but are not limited to,methyl group, methoxy carbonyl group, halogen, and a functional grouphaving halogen.

Specific examples of the monomer represented by the Chemical formula 2are illustrated below but are not limited thereto.

The monomer represented by the Chemical formula 2 can be synthesized asfollows and used. As illustrated in the following reaction formulae 1and 2, diisocyanate compound A-1 and naphthol A-2 are caused to reactunder the presence of an acid receptor such as amine or pyridine toobtain a reaction intermediate A-3. Thereafter, hydroxy alkylmethacrylate A-4 and A-3 are caused to react to obtain the monomerrepresented by the Chemical formula 2.

In another method, A-1 and A-4 were caused to react first and thereafterthe reaction product was caused to react with A-2 to obtain the monomerrepresented by the Chemical formula 2.

In yet another method, as illustrated in the reaction formula 3, thediisocyanate compound A-1, naphthol A-2, and hydroxy alkyl methacrylateA-4 were caused to react to obtain the monomer represented by theChemical formula 2.

To synthesize the copolymer mentioned above, it is preferable to use themethod using a radical polymerization initiator and more preferable touse the solution polymerization method conducting polymerizationreaction in a solution in terms of easiness of polymerization operationand molecular weight control.

As the solvent preferably usable to conduct radical polymerization inthe solution polymerization method, ketone-based solvents such asacetone, methylethyl ketone, methyl isobutyl ketone, acetic acidester-based solvents such as ethyl acetate and butyl acetate, aromatichydrocarbon-based solvents such as benzene, toluene, and xylene,isopropanol, ethanol, cyclohexane, tetrahydrofuran, dimethylformamide,dimethylsulfoxide, and hexamethyl phosphoamide are suitable. Of these,the ketone-based solvents and acetic acid ester-based solvents andalcohol-based solvents are preferable.

The radical polymerization initiator is not particularly limited and canbe selected to suit to a particular application.

Specific examples thereof include, but are not limited to, peroxy ketal,hydroperoxide, dialkylperoxide, diacylperoxide, peroxydicarbonate,peroxyester, cyano-based initiators such as azobisisobutylonitrile,azobis(2-methylbutylonitrile), azobis(2,2′-isovaleronitrile), andnon-cyano-based initiators such as dimethyl-2,2′-azobis isobutylate. Ofthese, organic peroxides and azo-based compounds are preferable and azocompounds are particularly preferable in terms of easiness of molecularweight control and low dissolution temperature.

In addition, the content of the radical polymerization initiator is notparticularly limited and can be determined to a particular application.The proportion thereof is preferably 1-10 percent by mass based on thetotal amount of the polymerizable monomer.

To control the molecular weight of the copolymer mentioned above, achain transfer agent may be optionally added.

Specific examples of the chain transfer agents include, but are notlimited to, mercapto acetate, mercapto propionate, 2-propane thiol,2-meracapto ethanol, thiophenol, dodecyl mercaptane, 1-dodecane thiol,and thioglycerol.

The polymerization temperature is not particularly limited and can beselected to suit to a particular application. It is preferably 50-150degrees C. and more preferably 60-100 degrees C. The polymerization timeis not particularly limited and can be suitably selected to suit to aparticular application. It is preferably 3-48 hours.

Content of Copolymer

The content of the copolymer in the ink of the present disclosure has noparticular limit and can be selected to suit to a particularapplication. The proportion is 0.05-10 percent by mass and morepreferably 0.3-5 percent by mass in solid portion. When the proportionis not less than 0.05 percent by mass, dispersibility and storageproperty are improved. When the proportion is not greater than 10percent by mass, a suitable range of viscosity can be obtained todischarge ink from heads.

The copolymer can be used as a dispersant for a pigment and an additivefor a pigment dispersion.

Usage of the copolymer as a dispersant for a pigment further improvesstorage stability of ink having a large proportion of a water-solubleorganic solvent.

The content of the copolymer used as a pigment dispersant is notparticularly limited and can be suitably selected to suit to aparticular application. It is preferably 1-100 parts by mass and morepreferably 5-80 parts by mass to 100 parts by mass of a pigment. Whenthe content is within this preferable range, a high image density andgood storage stability are obtained, which is advantageous.

Water

As the water for use in the ink of the present disclosure, for example,pure water and ultra pure water such as deionized water, ultrafilteredwater, reverse osmosis water, and distilled water are suitable.

The content of water in the ink has no particular limit and can besuitably selected to suit to a particular application. In terms ofdrying property and discharging reliability of the ink, the proportionis preferably 10-90 percent by mass and more preferably 20-60 percent bymass.

Coloring Material

Both pigments and dyes can be used as the coloring material for the inkof the present disclosure. However, when it comes to the adsorptionpower of the copolymer mentioned above to the coloring material,pigments are superior to dyes. Moreover, pigments are preferable interms of water resistance and light resistance.

Pigment

The pigments are not particularly limited. These can be selected to suitto a particular application. For example, inorganic pigments or organicpigments for black or color are suitable. These can be used alone or incombination.

The content of the pigment in ink is not particularly limited and can besuitably selected to suit to a particular application. The proportion ispreferably 0.5-20 percent by mass and more preferably 1-10 percent bymass.

Inorganic Pigment

Specific examples of the inorganic pigments include, but are not limitedto, titanium oxide, iron oxide, calcium oxide, barium sulfate, aluminumhydroxide, barium yellow, cadmium red, chrome yellow, and carbon black.

Specific examples of the pigments for black color include, but are notlimited to, carbon black (C.I. Pigment Black 7) such as furnace black,lamp black, acetylene black, and channel black, metals such as copperand iron (C.I. Pigment Black 11), and metal oxides such as titaniumoxides, and organic pigments such as aniline black (C.I. Pigment Black1).

Of various carbon blacks, it is suitable to use carbon blackmanufactured by a furnace method or channel method and having a primaryparticle diameter of 15 nm-40 nm, a specific surface area of 50-300 m²/gaccording to Brunauer-Emmett-Teller (BET) method, a dibutylphthalate(DPB) absorption oil amount of 40-150 ml/100 g, a volatile content offrom 0.5-10 percent, and pH of 2-9.

Organic Pigment

Specific examples of the organic pigments include, but are not limitedto, azo pigments (azo lakes, insoluble azo pigments, condensed azopigments, chelate azo pigments, etc.), polycyclic pigments(phthalocyanine pigments, perylene pigments, perinone pigments,anthraquinone pigments, quinacridone pigments, dioxazine pigments,indigo pigments, thioindigo pigments, isoindolinone pigments, andquinofuranone pigments, etc.), dye chelates (basic dye type chelate,acid dye type chelate), nitro pigments, nitroso pigments, and anilineblack.

Of these pigments, pigments having good affinity with water arepreferable in particular.

Specific examples of the azo pigments include, but are not limited to,azo lake, insoluble azo pigments, condensation azo pigments, and chelateazo pigments.

Specific examples of the polycyclic pigments include, but are notlimited to, phthalocyanine pigments, perylene pigments, perinonepigments, anthraquinone pigments, quinacridone pigments, dioxazinepigments, indigo pigments, thioindigo pigments, isoindolinone pigments,quinofuranone pigments, and, Rhodamine B lake pigments.

The dye chelate includes, but are not limited to, basic dye typechelate, and acidic dye type chelate.

The pigment for yellow is not particularly limited and can be selectedto a particular application.

Specific examples thereof include, but are not limited to, C.I. PigmentYellow 1, C.I. Pigment Yellow 2, C.I. Pigment Yellow 3, C.I. PigmentYellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. PigmentYellow 16, C.I. Pigment Yellow 17, C.I. Pigment Yellow 73, C.I. PigmentYellow 74, C.I. Pigment Yellow 75, C.I. Pigment Yellow 83, C.I. PigmentYellow 93, C.I. Pigment Yellow 95, C.I. Pigment Yellow 97, C.I. PigmentYellow 98, C.I. Pigment Yellow 114, C.I. Pigment Yellow 120, C.I.Pigment Yellow 128, C.I. Pigment Yellow 129, C.I. Pigment Yellow 138,C.I. Pigment Yellow 150, C.I. Pigment Yellow 151, C.I. Pigment Yellow154, C.I. Pigment Yellow 155, C.I. Pigment Yellow 174, and C.I. PigmentYellow 180.

The pigment for magenta is not particularly limited and can be selectedto a particular application.

Specific examples thereof include, but are not limited to, C.I. PigmentRed 5, C.I. Pigment Red 7, C.I. Pigment Red 12, C.I. Pigment Red 48(Ca), C.I. Pigment Red 48 (Mn), C.I. Pigment Red 57 (Ca), C.I. PigmentRed 57:1, C.I. Pigment Red 112, C.I. Pigment Red 122, C.I. Pigment Red123, C.I. Pigment Red 146, C.I. Pigment Red 168, C.I. Pigment Red 176,C.I. Pigment Red 184, C.I. Pigment Red 185, C.I. Pigment Red 202, andC.I. Pigment Violet 19.

The pigment for cyan is not particularly limited and can be selected tosuit to a particular application.

Specific examples thereof include, but are not limited to, C.I. PigmentBlue 1, C.I. Pigment Blue 2, C.I. Pigment Blue 3, C.I. Pigment Blue 15,C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:4, C.I. Pigment Blue 15:34,C.I. Pigment Blue 16, C.I. Pigment Blue 22, C.I. Pigment Blue 60, C.I.Pigment Blue 63, C.I. Pigment Blue 66, C.I. Pigment Pat Blue 4, and C.I.Pigment Pat Blue 60.

By using C.I. Pigment Yellow 74 as yellow pigment, C.I. Pigment Red 122and C.I. Pigment Violet 19 as magenta pigment, and C.I. Pigment Blue15:3 as cyan pigment, a well-balanced ink having excellent color toneand light resistance is obtained.

Self-Dispersible Pigment

The pigment for use in the present disclosure can be newly manufacturedfor the present disclosure.

In addition, in terms of coloring of obtained images, it is suitable touse a self-dispersible pigment and preferable to use an anionicself-dispersible pigment. The anionic self-dispersible pigment is formedby introducing an anionic functional group to the surface of a pigmentdirectly or via another atom group to stabilize dispersion.

As the pigment before dispersion is stabilized, variety of conventionalpigments can be used.

In the anionic functional group, more than a half of hydrogen ions aredissociated at pH 7.0.

Specific examples of the anionic functional groups include, but are notlimited to, a carboxyl group, a sulfo group, and a phosphonic acidgroup. Of these, to improve optical density of obtained images, acarboxyl group or a phosphonic acid group is preferable.

An anionic functional group is introduced into the surface of a pigmentby, for example, oxidation treatment of carbon black.

As the oxidization treatment, for example, hypochlorite, ozone water,hydrogen peroxide, chlorite, or nitric acid are used. Alternatively,surface treatment is suitable using a diazonium salt.

In addition, specific examples of the commercially available pigmenthaving a surface into which a hydrophilic group is introduced include,but are not limited to, CW-1, CW-2, and CW-3 (all manufactured by OrientChemical Industries Co., Ltd.), and CAB-O-JET200, CAB-O-JET300, andCAB-O-JET400 (all manufactured by Cabot Corporation).

The ink of the present disclosure can be produced by, for example,dispersing or dissolving, in an aqueous medium, water, a pigment, awater-soluble organic solvent, a coloring material, the copolymermentioned above, and optional other components followed by stirring andmixing. However, the producing method is not particularly limited. Thecopolymer may be used as a pigment dispersing resin when preparing apigment dispersion.

This dispersion is conducted by a sand mill, a homogenizer, a ball mill,a paint shaker, an ultrasonic dispersing agent, etc. The stirring andmixing can be conducted by a stirrer having a typical stirring wing, amagnetic stirrer, a high speed dispersing device, etc.

As for the production, coarse particles are preferably filtered with afilter, a centrifuge, etc. followed by degassing.

Dyes

As the dye mentioned above, dyes classified into acidic dyes, directdyes, basic dyes, reactive dyes, and food dyes in the color index can beused.

Specific examples of the acid dyes and food dyes include, but are notlimited to, C.I. Acid Black 1, 2, 7, 24, 26, and 94, C.I. Acid Yellow17, 23, 42, 44, 79, and 142, C.I. Acid Blue 9, 29, 45, 92, and 249, C.I.Acid Red 1, 8, 13, 14, 18, 26, 27, 35, 37, 42, 52, 82, 87, 89, 92, 97,106, 111, 114, 115, 134, 186, 249, 254, and 289, C.I. Food Black 1 and2, C.I. Food Yellow 3 and 4, and C.I. Food Red 7, 9, and 14.

Specific examples of the direct dyes include, but are not limited to, C.I. Direct Black 19, 22, 32, 38, 51, 56, 71, 74, 75, 77, 154, (168), and171, C.I. Direct Yellow 1, 12, 24, 26, 33, 44, 50, 86, 120, 132, 142,and 144, C.I. Direct Blue 1, 2, 6, 15, 22, 25, 71, 76, 79, 86, 87, 90,98, 163, 165, 199, and 202, C.I. Direct Red 1, 4, 9, 13, 17, 20, 28, 31,39, 80, 81, 83, 89, 225, and 227, and C.I. Direct Orange 26, 29, 62, and102.

Specific examples of the basic dyes include, but are not limited to,C.I. Basic Black 2 and 8, C.I. Basic Yellow 1, 2, 11, 13, 14, 15, 19,21, 23, 24, 25, 28, 29, 32, 36, 40, 41, 45, 49, 51, 53, 63, 64, 65, 67,70, 73, 77, 87, and 91, C.I. Basic Blue 1, 3, 5, 7, 9, 21, 22, 26, 35,41, 45, 47, 54, 62, 65, 66, 67, 69, 75, 77, 78, 89, 92, 93, 105, 117,120, 122, 124, 129, 137, 141, 147, and 155, and C.I. Basic Red 2, 12,13, 14, 15, 18, 22, 23, 24, 27, 29, 35, 36, 38, 39, 46, 49, 51, 52, 54,59, 68, 69, 70, 73, 78, 82, 102, 104, 109, and 112.

Specific examples of the reactive dyes include, but are not limited to,C.I. Reactive Black 3, 4, 7, 11, 12, and 17, C.I. Reactive Yellow 1, 5,11, 13, 14, 20, 21, 22, 25, 40, 47, 51, 55, 65, and 67, C.I. ReactiveBlue 1, 2, 7, 14, 15, 23, 32, 35, 38, 41, 63, 80, and 95, and C.I.Reactive Red 1, 14, 17, 25, 26, 32, 37, 44, 46, 55, 60, 66, 74, 79, 96,and 97.

Water-Soluble Organic Solvent

The water-soluble organic solvent for use in the ink of the presentdisclosure has an impact as a humectant to prevent dying of ink and/oras a permeating agent.

The water-soluble organic solvent has no particular limit and can beselected to suit to a particular application. Specific examples thereofinclude, but are not limited to, polyhydric alcohols such as ethyleneglycol, diethylene glycol, triethylene glycol, tetraethylene glycol,polyethylene glycol, propylene glycol, dipropylene glycol, tripropyleneglycol, polypropylene glycol, 1,3-butanediol, 3-methyl-1,3-butanediol,1,5-pentane diol, 1,6-hexanediol, glycerine, isopropylidene glycerol,trimethylolethane, trimethylolpropane, 1,2,4-butanetriol,1,2,3-butanetriol, 1,2,6-hexane triol, and petriol; polyhydric alcoholalkyl ethers such as ethylene glycol monoethyl ether, ethylene glycolmonobutyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycolmonomethyl ether, and propylene glycol monoethyl ether; polyhydricalcohol aryl ethers such as ethylene glycol monophenyl ether andethylene glycol monobenzyl ether; nitrogen-containing heterocycliccompounds such as 2-pyrrolidone, N-methyl-2-pyrrolidone,N-hydroxyethyl-2-pyrrolidone, 1,3-dimethylimidazolidinone,ε-caprolactam, and γ-butyrolactone; amides such as formamide,N-methylformamide, N,N-dimethylformamide, N,N-dimethyl-β-methoxypropionamide, and N,N-dimethyl-β-buthoxy propionamide; amines such asmonoethanolamine, diethanolamine, triethanolamine, monoethylamine,diethylamine, and triethylamine; sulfur-containing compounds such asdimethyl sulfoxide, sulfolane, and thiodiethanol;3-ethyl-3-hydroxymethyloxetane, propylene carbonate, and ethylenecarbonate. These can be used alone or in combination.

Of these, in terms of prevention of curling of plain paper, particularlypreferable are 3-ethyl-3-hydroxymethyloxetane, isopropylidene glycerol,N,N-dimethyl-β-methoxy propionamide, and N,N-dimethyl-β-buthoxypropionamide.

Of these, 1,3-butane diol, diethylene glycol,2,2,4-trimethyl-1,3-pentanediol, triethylene glycol, and glycerin have agood impact on prevention of defective discharging ascribable tomoisture evaporation.

Specific examples of the water-soluble organic solvents havingpermeation property and relatively low level of wettability include, butare not limited to, 2-ethyl-1,3-hexanediol [solubility: 4.2 percent (25degrees C.)] and 2,2,4-trimethyl-1,3-pentanediol [solubility: 2.0percent (25 degrees C.)].

Specific examples of the other polyol compounds include, but are notlimited to, aliphatic diols such as 2-ethyl-2-methyl-1,3-propanediol,3,3-dimethyl-1,2-butane diol, 2,2-diethyl-1,3-propane diol,2-methyl-2-propyl-1,3-propane diol, 2,4-dimethyl-2,4-pentane diol,2,5-dimethyl-2,5-hexane diol, and 5-hexene-1,2-diol.

The other permeating agent usable in combination can be any agentcapable of being dissolved in ink and adjusting to desired propertiesand are suitably selected to suit to particular applications.

Specific examples thereof include, but are not limited to, alkyl andaryl ethers of polyols such as diethylene glycol monophenylether,ethylene glycol monophenylether, ethylene glycol monoaryl ether,diethylene glycol monobutyl ether, diethylene glycol monophenyl ether,propylene glycol monobutyl ether, and tetraethylene glycol chlorophenylether and lower alcohols such as ethanol.

Sugar groups can be contained as a humectant, which is not awater-soluble organic solvent.

Specific examples of the sugar groups include, but are not limited to,monosaccharides, disaccharides, oligosaccharides (includingtrisaccharides and tetrasaccharides), and polysaccharides.

Specific examples thereof include, but are not limited to, glucose,mannose, fructose, ribose, xylose, arabinose, galactose, maltose,cellobiose, lactose, saccharose, trehalose, and maltotriose.

Polysaccharides represent sugar in a broad sense and contain materialsthat are present widely in nature, for example, α-cyclodextrine andcellulose.

In addition, specific examples of derivatives of these sugar groupsinclude, but are not limited to, reducing sugars (for example, sugaralcohols (represented by HOCH₂(CHOH)_(n)CH₂OH, where “n” represents aninteger of 2-5) of the sugar groups specified above, oxidized sugars(e.g., aldonic acid and uronic acid), amino acid, and thio acid. Ofthese, sugar alcohols are preferable and specific examples thereofinclude, but are not limited to, maltitol and sorbit.

When ink is used as ink for inkjet recording, the ratio of the pigmentand the water-soluble organic solvent has a large impact on dischargingstability of the ink discharged from a head. If the ratio of thewater-soluble organic solvent is small while the ratio of the solidpigment portion is large, moisture evaporation around the ink meniscusof the nozzle tends to be accelerated, thereby causing defectivedischarging.

The content of the water-soluble organic solvent in ink has noparticular limit and can be suitably selected to suit to a particularapplication. The proportion is preferably 10-60 percent by mass and morepreferably 20-60 percent by mass. When the proportion is not less than10 percent by mass, discharging stability of ink can be secured. Whenthe proportion is not greater than 60 percent by mass, drying propertyis enhanced. When the proportion is within the preferable range, dryingproperty and discharging reliability are extremely good.

Other Components

The other components that can be used in the ink of the presentdisclosure has no particular limit and can be suitably selected to suitto a particular application. For example, surfactants, pH regulators,water-dispersible resins, preservatives and fungicides, corrosioninhibitors, antioxidants, ultraviolet absorbers, oxygen absorbers, andphotostabilizing agents are suitable.

Surfactant

The surfactant has no particular limit and can be suitably selected tosuit to a particular application. For example, anionic surfactants,cationic surfactants, nonionic surfactants, amphoteric surfactants, andfluoro-surfactants are suitable. Of these, nonionic surfactants andfluoro-surfactants are particularly preferable.

Specific examples of the anionic surfactant include, but are not limitedto, alkyl aryl sulfonic acid salts, alkyl naphthalene sulfonic acidsalts, alkyl phosophoric acid salts, alkyl sulfuric acid salts, alkylsulphonic acid salts, alkyl ether sulfuric acid salts, alkyl sulphosuccinic acid salts, alkyl ester sulfuric acid salts, alkyl benzenesulfonic acid salts, alkyl diphenyl ether disulphonic acid salts, alkylaryl ether phosphoric acid salts, alkyl aryl ether sulfuric acid salts,alkyl aryl ether ester sulfuric acid salts, olefin sulfonic acid salts,alkane olefin sulfocnic acid salts, polyoxyethylene alkyl etherphosphoric acid salts, polyoxyethylene alkyl ether sulfuric acid estersalts, ether carboxylate, sulfosuccinic acid salts, α-sulfoalicyclicacid esters, aliphatic acid salts, condensation products of a higheraliphatic acid and an amino acid, and naphthene acid salts.

Specific examples of the cationic surfactants include, but are notlimited to, alkyl amine salts, dialkyl amine salts, aliphatic aminesalts, benzalkonium salts, quaternary amonium salts, alkyl pyridiniumsalts, imidazolinium salts, sulfonium salts, and phosphonium salts.

Specific examples of the nonionic surfactants include, but are notlimited to, acetylene glycol-based surfactants, polyoxyethylene alkylethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkylesters,and polyoxyethylene sorbitane aliphatic acid esters.

Specific examples of the amphoteric surfactants include, but are notlimited to, imidazoline derivatives such as imidazolinium betaine,dimethyl alkyl lauryl betaine, alkyl glycine, and alkyl di(aminoethyl)glycine.

As the fluorosurfactants, for example, the materials represented byChemical formulae I, II, and III are suitable.CF₃CF₂(CF₂CF₂)_(m)CH₂—CH₂O(CH₂CH₂O)_(n)H  Chemical formula I

In the Chemical formula I, a symbol “m” represents 0 and an integer of1-10. A symbol “n” represents an integer of 1-40.

In the Chemical formula II, Rf represents a fluoro-containing group, m,n, and p each, represent integers.

As the fluoro-containing group, for example, perfluoroalkyl groups arepreferable. In particular, those having 1-10 carbon atoms are preferableand those having 1-3 carbon atoms are more preferable. An example isC_(j)F_(2j-1) (where j represents an integer of 1-10).

Specific examples thereof include, but are not limited to, CF₃, CF₂CF₃,C₃F₇, and C₄F₉. Of these, CF₃ and CF₂CF₃ are particularly preferable. Inaddition, it is preferable that “n” be an integer of 1-4, “m” be aninteger of 6-25, and “p” be an integer of 1-4.

In the Chemical formula III, Rf represents a fluoro-containing group, qrepresents an integer.

As the fluoro-containing group, as in the case of the Chemical formulaII, a perfluoroalkyl group is preferable. For example, CF₃, CF₂CF₃,C₃F₇, and C₄F₉ are suitable. R₂ ⁺ represents a cation group, forexample, a quaternary ammonium group, an alkali metal ion of sodium,potassium, etc., a triethyl amine and a triethanol amine are suitable.Of these, quaternary ammonium is particularly preferable. R₁ ⁻represents an anionic group, for example, COO⁻, SO₃ ⁻, SO₄ ⁻, and PO₄ ⁻are suitable. “q” is preferably an integer of 1-6.

Any suitably synthesized fluoro-surfactant can be used. Productsavailable on the market are also usable.

Specific examples of the products available on the market include, butare not limited to, SURFLON 5-111, SURFLON S-112, SURFLON S-121, SURFLONS-131, SURFLON S-132, SURFLON S-141, and SURFLON S-145 (all manufacturedby ASAHI GLASS CO., LTD.); FLUORAD FC-93, FC-95, FC-98, FC-129, FC-135,FC-170C, FC-430, and FC-431 (all manufactured by SUMITOMO 3M); MEGAFACEF-470, F1405, and F-474 (all manufactured by DIC CORPORATION); ZONYLTBS, FSP, FSA, FSN-100, FSN, FSO-100, FSO, FS-300 UR (all manufacturedby E. I. du Pont de Nemours and Company; FT-110, FT-250, FT-251,FT-400S, FT-150, and FT-400SW (all manufactured by NEOS COMPANYLIMITED); PF-151N manufactured by OMNOVA Solutions Inc.), and UNIDYNEDSN-403N, manufactured by DAIKIN INDUSTRIES). Of these, ZONYL FS-300,FSN, FSO-100, and FSO (all manufactured by E. I. du Pont de Nemours andCompany) are particularly suitable in terms of the reliability andimprovement on coloring.

The content of the surfactant in ink has no particular limit and can besuitably selected to suit to a particular application. The proportionpreferably 0.01-5.0 percent by mass and more preferably 0.5-3 percent bymass. When the proportion is not greater than 5.0 percent by mass,permeation into a recording medium is good, so that lowering of imagedensity and occurrence of strike-through can be prevented.

pH Regulator

The pH regulator can be any agent capable of adjusting the pH in therange of 8.5-11 without having an adverse impact on formulated ink andsuitably selected to suit to a particular application.

Specific examples thereof include, but are not limited to, alcoholamines, hydroxides of alkali metal elements, hydroxides of ammonium,phosphonium hydroxides, and alkali metal carbonates.

Specific examples of the alcohol amines include, but are not limited to,diethanol amine, triethanol amine, and 2-amino-2-ethyl-1,3-propane diol.

Specific examples of the hydroxides of alkali metal elements include,but are not limited to, lithium hydroxide, sodium hydroxide, andpotassium hydroxide.

Specific examples of the hydroxides of ammonium include, but are notlimited to, ammonium hydroxide and quaternary ammonium hydroxide.

A specific example of the phosphonium hydroxides is quaternaryphosphonium hydroxide.

Specific examples of the alkali metal carbonates include, but are notlimited to, lithium carbonate, sodium carbonate, and potassiumcarbonate.

Water-Dispersible Resin

The water-dispersible resin mentioned above has excellent film-forming(image forming) property, water repellency, water-resistance, andweather resistance. Therefore, these are suitable for image recordingrequiring good water-resistance and high image density (good coloringproperty).

Examples are condensation-based synthetic resins, addition-basedsynthetic resins, and natural polymers.

Specific examples of the condensation-based synthetic resins include,but are not limited to, polyester resins, polyurethane resins, polyepoxyresins, polyamide resins, polyether resins, poly(meth)acrylic resins,acrylic-silicone resins, and fluorine-containing resins.

Specific examples of the addition-based synthetic resins include, butare not limited to, polyolefin resins, polystyrene-based resins,polyvinyl alcohol-based resins, polyvinyl ester-based resins,polyacrylic acid-based resins, and unsaturated carboxylic acid-basedresins.

Specific examples of the natural polymer include, but are not limitedto, celluloses, rosins, and natural rubber.

Of these, polyurethane resin particulates, acrylic-silicone resinparticulates, and fluorine-containing resin particulates are preferable.

The average particle diameter (D50) of the water-dispersible resin isrelated to viscosity of a liquid dispersion. If the compositions are thesame, viscosity of the same solid portion increases as the particlediameter decreases.

The average particle diameter (D50) of the water-dispersible resin hasno particular limit and can be suitably selected to suit to a particularapplication. To avoid excessively high viscosity, 50 μm or greater ispreferable.

In addition, when the particle diameter is around several tens μm, it isunusable because the size is larger than the size of the nozzle of aninkjet head. If the particle size is less than the nozzle size but largeparticles are present in ink, discharging stability deteriorates. Theaverage particle diameter (D50) is preferably 200 nm or less not todegrade discharging stability of ink.

In addition, preferably the water-dispersible resin has a feature offixing the water-dispersible coloring material on paper and forms a filmat room temperature, which improves fixing property of the coloringmaterial.

Therefore, the minimum film-forming temperature (MFT) of thewater-dispersible resin is preferably 30 degrees C. or lower.

In addition, when the glass transition temperature of thewater-dispersible resin is −40 degrees C. or lower, viscosity of theresin film increases, thereby increasing tackiness of printed matter.Therefore, the glass transition temperature of the water-dispersibleresin is preferably about −30 degrees C. or higher.

The content of the water-dispersible resin in ink has no particularlimit and can be suitably selected to suit to a particular application.The proportion preferably 1-15 percent by mass and more preferably 2-7percent by mass in solid portion.

Preservatives and Fungicides

Specific examples of the preservatives and fungicides include, but arenot limited, dehydrosodium acetate, sodium sorbinate-2-pyridinethiol-1-oxide sodium, sodium benzoate, and pentachlorophenol sodium.

Corrosion Inhibitor

Specific examples of the corrosion inhibitors include, but are notlimited to, acid sulfite, thiosodium sulfate, thiodiglycolate ammon,diisopropyl ammonium nitrite, pentaerythritol tetranitrate, anddicyclohexyl ammonium nitrite.

Antioxidant

Specific examples of the antioxidants include, but are not limited to,phenol-based antioxidants (including hindered phenol-basedantioxidants), amino-based antioxidants, sulfur-based antioxidants, andphosphorous-based antioxidants.

Ultraviolet Absorber

Specific examples of the ultraviolet absorbers include, but are notlimited to, benzophenone-based ultraviolet absorbers,benzotriazole-based ultraviolet absorbers, salicylate-based ultravioletabsorbers, cyanoacrylate-based ultraviolet absorbers, and nickel complexsalt-based ultraviolet absorbers.

Use Application of Ink

The ink of the present disclosure is suitable for inkjet recording,spray-coating, relief printing plate printing, intaglio printing,stencil printing, writing materials, and stamp. In particular, the inkis suitable for inkjet recording.

Ink Cartridge

The ink cartridge of the present disclosure includes the ink mentionedabove, a container to accommodate the ink, and other optional othermembers.

The container has no particular limit. The form, the structure, thesize, and the material thereof can be suitably determined to suit to aparticular application. For example, a container having an ink bag madeof aluminum laminate film, a resin film, etc. is suitable. Next, the inkcartridge is described in detail with reference to FIGS. 1 and 2.

FIG. 1 is a diagram illustrating an example of the ink cartridge. FIG. 2is a diagram illustrating the ink cartridge illustrated in FIG. 1including the housing thereof. In an ink cartridge 200, ink is suppliedto an ink bag 241 through an ink inlet 242, the air remaining in the inkbag 241 is discharged, and thereafter the ink inlet 242 is closed byfusion. When in use, an ink outlet 243 made of rubber is pierced by theneedle installed onto an inkjet recording device to supply the ink intothe device. The ink bag 241 is made of a packaging material such asaluminum laminate film having no air permeability. The ink bag 241 isaccommodated in a cartridge housing 244 made of plastic as illustratedin FIG. 2 and detachably attachable to various inkjet recording devicesas the ink cartridge 200.

Having generally described preferred embodiments of this invention,further understanding can be obtained by reference to certain specificexamples which are provided herein for the purpose of illustration onlyand are not intended to be limiting. In the descriptions in thefollowing examples, the numbers represent weight ratios in parts, unlessotherwise specified.

EXAMPLES

Next, the present disclosure is described in detail with reference toExamples and Comparative Examples but not limited thereto. “Parts” and“percent” in Examples including Table 1 are “parts by weight” and“percent by mass” unless otherwise specified. The values in Tables 2 and3 are also represented in parts by mass.

Measuring of Molecular Weight of Copolymer

The molecular weight of the copolymers obtained in Examples andComparative Examples were obtained as follows:

The molecular weight of the copolymers was measured by a gel permeationchromatography (GPC) under the following conditions:

Device: GPC-8020 (manufactured by TOSOH CORPORATION)

Column: TSK G2000 HXL and G4000 HXL (manufactured by TOSOH CORPORATION)

Temperature: 40 degrees C.

Solvent: tetrahydrofuran (THF)

Flow speed: 1.0 mL/minute

Next, the number average molecular weight Mn and the mass averagemolecular weight Mw were calculated from the molecular weightdistribution of the copolymer obtained by the measuring by using themolecular weight calibration curve obtained based on a simple dispersionpolystyrene standard sample.

Synthesis Example of Copolymer

Monomer Synthesis 1: Synthesis of Monomer M-3

50.5 g (300 mmol) of hexamethylene diisocyanate and 30.4 g (300 mmol)were dissolved in 300 mL of dried toluene and the obtained solution washeated to 105 degrees C. under stirring in argon atmosphere. Next, asolution in which 43.3 g (300 mmol) of 2-naphtol was dissolved in 1,500mL of dried toluene was slowly dripped and the resultant was stirred at105 degrees C. for two hours. Subsequent to cooling down to roomtemperature and filtration of precipitates, the solvent was distilledaway from the retrieved filtrate to obtain a white solid material. Thismaterial was charged in 200 mL of hexane followed by stirring at roomtemperature for one hour. The white solid material was filtrated toobtain 53.0 g of a reaction intermediate represented by the followingChemical formula 3.

20.8 g (160 mmol) of 2-hydroxyethyl methacrylate was dissolved in 80 mLof methylethyl ketone and stirred at room temperature in argonatmosphere. Next, 0.03 g of dibutyl tin dilaurate was dripped to thesolution and heated to 50 degrees C. under stirring. Thereafter, asolution in which 50.0 g of the reaction intermediate represented by theChemical formula 3 was dissolved in 120 mL of methylethyl ketone wasslowly dripped followed by stirring at 50 degrees C. for two hours.Next, the resultant was cooled down to room temperature to filterundissolved matter and the solvent was distilled away from the filtrateto obtain a crude paste. This paste was refined by silica gel columnchromatography (methylene chloride/ethylene acetate=6/1) to obtain 48.0g of the target of monomer M-3.

Monomer Synthesis 2: Synthesis of Monomer M-5

18.6 g (160 mmol) of 2-hydroxyethyl acrylate was dissolved in 80 mL ofmethylethyl ketone and stirred at room temperature in argon atmosphere.Next, 0.03 g of dibutyl tin dilaurate was dripped to the solution andheated to 50 degrees C. under stirring. Thereafter, a solution in which50.0 g of the reaction intermediate represented by the Chemical formula3 was dissolved in 120 mL of methylethyl ketone was slowly drippedfollowed by stirring at 50 degrees C. for two hours. Next, the resultantwas cooled down to room temperature to filter undissolved matter and thesolvent was distilled away from the filtrate to obtain a crude paste.This paste was refined by silica gel column chromatography (methylenechloride/ethylene acetate=6/1) to obtain 45.9 g of the target monomerM-5.

Monomer Synthesis 3: Synthesis of Mixture of Monomer M-8 and Monomer M-9

63.1 g (300 mmol) of trimethylhexamethylene diisocyanate (2,2,4-,2,2,4,4-, isomer mixture, manufactured by Tokyo Chemical Industry Co.Ltd.) and 30.4 g (300 mmol) of triethylamine were dissolved in 300 mL ofdried toluene and the solution was heated to 105 degrees C. understirring in argon atmosphere. Next, a solution in which 43.3 g (300mmol) of 2-naphtol was dissolved in 1,500 mL of dried toluene was slowlydripped and the resultant was stirred at 105 degrees C. for two hours.Subsequent to cooling down to room temperature and filtration ofprecipitates, the solvent was distilled away from the filtrate to obtaina white solid material.

200 mL of hexane was charged to this material followed by stirring atroom temperature for one hour. The white solid material was filtrated toobtain 60.5 g of a reaction intermediate mixture represented by Chemicalformulas 4 and 5.

20.8 g (160 mmol) of 2-hydroxyethyl methacrylate was dissolved in 80 mLof methylethyl ketone and stirred at room temperature in argonatmosphere. Next, 0.03 g of dibutyl tin dilaurate was dripped to thesolution and heated to 50 degrees C. under stirring. Thereafter, asolution in which 57.0 g of the reaction intermediate mixturerepresented by the Chemical formulae 4 and 5 was dissolved in 120 mL ofmethylethyl ketone was slowly dripped followed by stirring at 50 degreesC. for two hours. Next, the resultant was cooled down to roomtemperature to filter undissolved matter and the solvent was distilledaway from the retrieved filtrate to obtain a crude paste. This paste wasrefined by silica gel column chromatography (methylene chloride/ethyleneacetate=6/1) to obtain 49.7 g of the target monomer mixture of M-8 andM-9.

Synthesis Example 1: Synthesis of Copolymer CP-1

12.4 parts (172 mmol) of acrylic acid and 47.6 parts (108 mmol) of themonomer M-3 were dissolved in 420 mL of dried methylethyl ketone toprepare a monomer solution.

10 percent of the monomer solution was heated to 75 degrees C. in anargon atmosphere. Thereafter, a solution in which 2.3 parts of2,2′-azobis(isobutylonitrile) (AIBN) and 0.2 parts of α-thioglycerolwere dissolved in the rest (90 percent) of the monomer solution wasdripped to the heated monomer solution in 2.5 hours followed by stirringat 75 degrees C. for six hours. The resultant was cooled down to roomtemperature and the thus-obtained reaction solution was charged tohexane. The precipitate was filtrated followed by drying with a reducedpressure to obtain 58.5 parts of Copolymer CP-1 (Mw: 22,000).

Synthesis Examples 2-18: Synthesis of Copolymers CP-2-CP-18

Copolymer CP-2 to Copolymer CP-18 were obtained in the same manner as inthe synthesis of Copolymer CP-1 except that the monomer, the number ofparts, and the polymerization temperature in the synthesis of CopolymerCP-1 were changed to Monomers M-3, M-5, M-8, and M-9, anionic monomers,other monomers, the number of parts, and the polymerization temperaturesshown in each column of Synthesis Examples 2-18 of Table 1 and AIBN andthioglycerol serving as the chain transfer adjusting agent were used asshown in Table 1.

Mw and the produced amount of each copolymer are as shown in Table 1. AAand MAA in the column of anionic monomer in Table 1 respectivelyrepresent acrylic acid and methacrylic acid.

Preparation Example of Pigment Dispersion

Preparation of Pigment Dispersion PD-1

4.0 parts of copolymer CP-1 was dissolved in 80.0 parts of a pure wateraqueous solution of tetraethyl ammonium hydroxide (TEAOH) in such amanner that pH was 8.0. 16.0 parts of carbon black (NIPEX150,manufactured by Degussa AG) was added to 84.0 parts of the aqueoussolution of the thus-obtained copolymer followed by stirring for 12hours.

The obtained mixture was subject to circulation dispersion at aperipheral speed of 10 m/s for one hour using a disk type bead mill (KDLtype, media: zirconia ball having a diameter of 0.1 mm, manufactured byShinmaru Enterprises Corporation) followed by filtration by a membranefilter having an opening diameter of 1.2 micro meter. Thereafter, purewater was added for adjustment to obtain 97.0 parts of a pigmentdispersion element PD-1 (pigment solid portion concentration: 16percent).

Preparation of Pigment Dispersion PD-2-PD-23

Pigment dispersion PD-2-PD-23 were obtained in the same manner as in thepreparation of Pigment dispersion PD-1 except that the copolymer, the pHregulator, the kind and the content of the pigment, and the content ofthe pure water were changed as shown in each column of PD-2-PD-23 ofTable 2.

TEAOH in Table 1 is tetraethyl ammonium hydroxide, NaOH is sodiumhydroxide, and DEA is diethanol amine.

In addition, the color pigments used were as follows.

Pigment Blue 15:3: CHROMOFINE BLUE A-220JC, manufactured byDainichiseika Color & Chemicals Mfg. Co., Ltd.

Pigment Red 122: Toner Magenta E002, manufactured by Clariant)

Pigment Yellow 74: Fast Yellow, manufactured by Dainichiseika Color &Chemicals Mfg. Co., Ltd.

Preparation Example of Ink

Preparation of Example 1: Ink GJ-1

40.0 parts of Pigment dispersion PD-1, 10.0 parts of glycerin, 20.0parts of 1,3-butane diol, 1.0 part of 2-ethyl-1,3-hexane diol, 1.0 partof 2,2,4-trimethyl-1,3-pentane diol, 1.0 part of UNIDYNE™ DSN-403N(manufactured by DAIKIN INDUSTRIES, Ltd.), and 27.0 parts of pure waterwere mixed followed by stirring for one hour. The mixture was filteredby a membrane filter having an opening of 1.2 μm to obtain Ink GJ-1 ofthe present disclosure.

Preparation of Example 2-Example 23: Ink GJ-2-GJ-23

Ink GJ-2-GJ-23 were obtained in the same manner as in the preparation ofInk GJ-1 except that the pigment dispersion, the water-soluble solvent,and the kind and the content of the surfactant were changed as shown ineach column of Example 2-Example 23 of Table 3.

Comparative Example 1: Preparation of Ink RGJ-1

1.20 g of acrylic acid and 7.12 g of the monomer represented by thefollowing Chemical formula 6 were dissolved in 40 mL of driedmethylethyl ketone to prepare a monomer solution. 10 percent of themonomer solution was heated to 75 degrees C. in an argon atmosphere.Thereafter, a solution in which 0.273 g of 2,2′-azobis(isobutylonitrile)was dissolved in the rest (90 percent) of the monomer solution wasdripped to the heated monomer solution in 1.5 hours followed by stirringat 75 degrees C. for six hours. Subsequent to being cooled down to roomtemperature, the thus-obtained reaction solution was charged to hexaneto precipitate a copolymer followed by filtration and drying under areduced pressure to obtain 4.82 g of Copolymer RCP-1 (Mw: 7,500).

Thereafter, Pigment dispersion RPD-1 was obtained in the same manner asin the preparation of Pigment dispersion PD-1 of Example 1 except thatthe Comparative copolymer RCP-1 was used instead of the Copolymer CP-1.

Thereafter, Ink RGJ-1 was obtained in the same manner as in thepreparation of the Ink GJ-1 of Example 1 except that the Pigmentdispersion element RPD-1 was used instead of the Pigment dispersionPD-1.

Comparative Example 2: Preparation of Ink RGJ-2

Thereafter, Pigment dispersion RPD-2 was obtained in the same manner asin the preparation of Pigment dispersion PD-21 of Example 21 except thatthe Comparative copolymer RCP-1 was used instead of the Copolymer CP-1.

Thereafter, Ink RGJ-2 was obtained in the same manner as in thepreparation of the Ink GJ-21 of Example 21 except that the Pigmentdispersion RPD-2 was used instead of the Pigment dispersion PD-21.

Comparative Example 3: Preparation of Ink RGJ-3

Thereafter, Pigment dispersion RPD-3 was obtained in the same manner asin the preparation of Pigment dispersion PD-22 of Example 22 except thatthe Comparative copolymer RCP-1 was used instead of the Copolymer CP-1.

Thereafter, Ink RGJ-3 was obtained in the same manner as in thepreparation of the Ink GJ-22 of Example 22 except that the Pigmentdispersion RPD-3 was used instead of the Pigment dispersion PD-22.

Comparative Example 4: Preparation of Ink RGJ-4

Thereafter, Pigment dispersion RPD-4 was obtained in the same manner asin the preparation of Pigment dispersion PD-23 of Example 23 except thatthe Comparative copolymer RCP-1 was used instead of the Copolymer CP-1.

Thereafter, Ink RGJ-4 was obtained in the same manner as in thepreparation of the Ink GJ-23 of Example 23 except that the Pigmentdispersion RPD-4 was used instead of the Pigment dispersion PD-23.

Comparative Example 5: Preparation of Ink RGJ-5

80 g of 2-phenoxyethyl methacrylate as a monomer, 3.7 g of3-mercapto-1-propanol as a chain transfer agent, and 0.3 g of2,2-azobis(2,4-dimethyl valero nitrile) as an initiator were dissolvedin 160 mL of tetrahydrofuran (THE) followed by heating to 65 degrees C.to conduct reaction in nitrogen atmosphere for seven hours. Thethus-obtained solution was naturally cooled down and 80 mg of dibutyltin (IV) dilaurate and a catalyst amount of hydroquinone were addedthereto. Thereafter, 10.0 g of 2-methacryloyloxy ethylisocyanate wasdripped. The resultant was heated to 50 degrees C. to conduct reactionfor 2.5 hours. Thereafter, the resultant was re-precipitated by asolvent mixture of water and methanol for refinement to obtain 71 g ofmacromonomer MM-1 (mass average molecular weight (Mw): 4,000, numberaverage molecular weight (Mn): 1,900).

Thereafter, 20 g of methylethylketone was heated to 75 degrees C. innitrogen atmosphere. A solution in which 1.16 g of dimethyl-2,2′-azobisisobutylate, 9 g of the macromonomer MM-21, 1.8 g of p-styrene sulfonicacid, and 49.2 g of methylmethacrylate were dissolved in 40 g ofmethylethylketone was dripped to the heated methylethylketone in threehours. After the dripping, the reaction was caused to continue anotherhour.

Thereafter, a solution in which 0.6 g of methylethylketone was dissolvedin 0.2 g of dimethyl-2,2′-azobisisobutylate was added and heated to 80degrees C. and kept at 80 degrees C. for four hours under stirring.Furthermore, a solution in which 0.2 g of dimethyl-2,2′-azobisisobutylate was dissolved in 0.6 g of methylethylketone was addedfollowed by stirring for six hours under heating. Subsequent to beingcooled down, the thus-obtained reaction solution was charged to hexaneto precipitate a graft polymer followed by filtration and drying toobtain Comparative copolymer RCP-2.

Thereafter, Pigment dispersion RPD-5 was obtained in the same manner asin the preparation of Pigment dispersion PD-1 except that theComparative copolymer RCP-2 was used instead of the Copolymer CP-1.

Thereafter, Ink RGJ-5 was obtained in the same manner as in thepreparation of the Ink GJ-1 except that the Pigment dispersion elementRPD-5 was used instead of the Pigment dispersion element PD-1.

Comparative Example 6: Preparation of Ink RGJ-6

Synthesis of Monomer

72.0 g (500 mmol) of 2-naphthol and 125.0 g (1,000 mmol) of ethyleneglycol mono-2-chloroethyl ether were dissolved in 500 mL ofN-methyl-2-pyrrolidinone followed by stirring for one hour at roomtemperature. Moreover, the solution was stirred at 110 degrees C. for 10hours and cooled down to room temperature. 2,500 mL of pure water wasadded to the thus-obtained reaction solution. Subsequent to one-hourstirring at room temperature, a precipitated solid material was filteredand dried with a reduced pressure.

70.0 g of the solid material obtained in the reaction specified aboveand 45.0 g (450 mmol) of triethylamine were dissolved in 250 mL oftetrahydrofuran followed by 30-minute stirring in ice bath. 36.6 g (350mmol) of methacryloyl was slowly dripped followed by 3-hour stirring inice bath. 250 mL of ethyl acetate and 100 mL of pure water were added tothe thus-obtained solution for rinsing with water. Thereafter, the ethylacetate layer was isolated followed by rinsing with saturated saltwater. The ethyl acetate layer was isolated again followed by dryingwith magnesium sulfate and the solvent was distilled away. The remainderwas refined by silica gel column chromatography to obtain 80.5 g of amonomer represented by the following Chemical formula 7.

Synthesis of Copolymer RCP-3

12.0 g of methylethylketone was placed in a flask equipped with astirrer and a condenser and heated to 72 degrees C. in argon atmosphere.Thereafter, a solution in which 2.4 g (8.00 mmol) of the monomerrepresented by the Chemical formula 7, 1.2 g (13.9 mmol) of methacrylicacid, 8.4 g (47.6 mmol) of benzyl methacrylate, 0.128 g (0.56 mmol) of2,2′-azobis(isobutyric acid)dimethyl were dissolved in 6.0 g ofmethylethyl ketone was dripped in three hours. After the dripping, thereaction was caused to continue for another hour. A solution in which0.06 g (0.26 mmol) of 2,2′-azobis(isobutyric acid)dimethyl was dissolvedin 2.0 g of methylethyl ketone was added and thereafter the system washeated to 78 degrees C. and stirred for four hours. Thereafter,re-precipitation was repeated twice using hexane. After refining acopolymer, the copolymer was filtered and dried with a reduced pressureto obtain 11.6 g of Copolymer RCP-3 (Mw: 34,000).

Preparation of Pigment Dispersion RPD-6

4.0 parts of the Copolymer RCP-3 was dissolved in a liquid mixture of1.9 parts of 35 percent tetraethyl ammonium hydroxide, 50.0 parts of3-methoxy-N,N′-dimethyl propinoneamide, and 28.1 parts of pure water.

16.0 parts of carbon black (NIPEX150, manufactured by Degussa AG) wasadded to 84.0 parts of the aqueous solution of the Copolymer RCP-3followed by stirring for 12 hours. The thus-obtained mixture was subjectto circulation dispersion at a peripheral speed of 10 m/s for one hourusing a disk type bead mill (KDL type, media: zirconia ball having adiameter of 0.1 mm, manufactured by Shinmaru Enterprises Corporation)followed by filtration by a membrane filter having an opening diameterof 1.2 micro meter. Thereafter, pure water was added for adjustment toobtain 95.0 parts of a pigment dispersion RPD-6 (pigment solid portionconcentration: 16 percent).

Preparation of Ink RGJ-6

40.0 parts of Pigment dispersion RPD-6, 10.0 parts of glycerin, 10.0parts of 1,3-butane diol, 1.0 part of 2-ethyl-1,3-hexane diol, 1.0 partof 2,2,4-trimethyl-1,3-pentane diol, 1.0 part of UNIDYNE™ DSN-403N(solid portion: 100 percent, manufactured by DAIKIN INDUSTRIES, Ltd.),and 37.0 parts of pure water were mixed followed by stirring for onehour. The mixture was filtered by a membrane filter having an openingdiameter of 1.2 μm to obtain Ink RGJ-6.

Storage stability of the pigment dispersions prepared in Examples andComparative Examples were evaluated in the following manner.

Storage Stability of Pigment Dispersion

A glass container was filled with each pigment dispersion and stored at70 degrees C. for two weeks. The change rate of the viscosity after thestorage to the viscosity before the storage was obtained from thefollowing relation and evaluated according to the following criteria. G(Good), A (Acceptable), and M (Marginal) are suitable in terms ofpractical use.

Viscosity was measured by a viscometer (RE80L, manufactured by TOKISANGYO CO., LTD.) to measure viscosity of the ink at 25 degrees C. at 50rotations.Change rate of viscosity (percent)=[(Viscosity of pigment dispersionafter storage−Viscosity of pigment dispersion before storage)/viscosityof pigment dispersion before storage}×100

Evaluation Criteria

G (Good): Change rate of viscosity within + or −5 percent

A (Acceptable): Change rate of viscosity within the range of from −8percent to less than −5 percent and more than 5 percent to 8 percent

M (Marginal): Change rate of viscosity within −10 percent to less than−8 percent and greater than 8 percent to 10 percent.

P (Poor): Change rate of viscosity within the range of from less than−10 percent to −30 percent and more than 10 percent to 30 percent

I (Intolerable): Change rate of viscosity less than −30 percent orgreater than 30 percent (gelated to the degree that evaluation was notpossible)

Properties of the inks prepared in Examples and Comparative Exampleswere measured and evaluated in the following manner.

Storage Stability of Ink

An ink cartridge was filled with each ink and stored at 70 degrees C.for one week. The change rate of the viscosity after the storage to theviscosity before the storage was obtained from the following relationand evaluated according to the following criteria. G (Good), A(Acceptable), and M (Marginal) are suitable in terms of practical use.

Viscosity was measured by a viscometer (RESOL, manufactured by TOKISANGYO CO., LTD.) to measure the viscosity of the ink at 25 degrees C.at 50 rotations.The change rate of viscosity (percent)=[(Viscosity of ink afterstorage−viscosity of ink before storage)/viscosity of ink beforestorage]×100

Evaluation Criteria

G (Good): Change rate of viscosity within +5 percent or −5 percent

A (Acceptable): Change rate of viscosity within the range of from −8percent to less than −5 percent and more than 5 to 8 percent

M (Marginal): Change rate of viscosity within −10 percent to less than−8 percent and greater than 8 percent to 10 percent.

P (Poor): Change rate of viscosity within the range of from less than−10 percent to −30 percent and more than 10 percent to 30 percent

I (Intolerable): Change rate of viscosity less than −30 percent orgreater than 30 percent (gelated to the degree that evaluation was notpossible)

Image Density

An inkjet printer (IPSiO GX5000) was filled with each ink at 23 degreesC. and 50 percent RH. A chart including general symbols of 64 point JISX 0208 (1997), 2223 created by utilizing Microsoft Word 2000(manufactured by Microsoft Corporation) was printed on plain paper 1(Xerox 4200, manufactured by Xerox Corporation) and paper 2 (MyPaper,manufactured by Ricoh Company Ltd.). The symbol portion on image surfacewas measured by X-Rite 938 (manufactured by X-Rite Inc.) and evaluatedaccording to the following criteria.

G (Good), A (Acceptable), and M (Marginal) are suitable for practicaluse.

The print mode used was: A modified mode in which “Plain Paper—StandardFast” was modified to “No Color Calibration” from the user setting forplain paper by the driver installed onto the printer.

Incidentally, the symbols of JIS X 0208 (1997), 2223 include squares forthe exterior with the inside thereof entirely painted with ink.

Evaluation Criteria

G (Good): 1.25 or higher

A (Acceptable): 1.20 to less than 1.25

M (Marginal): 1.10 to less than 1.20

P (Poor): Less than 1.10

I (Intolerable): pigment was gelated and not dispersed in ink,impossible to print symbols.

TABLE 1 Chemical Anionic Monomer formula 2 monomer other than aboveCopolymer Kind Part Kind Part Kind Part Synthesis CP-1  M-3 47.6 AA 12.4— — Example 1: Synthesis CP-2  M-5 45.4 MAA 14.6 — — Example 2:Synthesis CP-3  M-8, M-9 42.8 AA 12.7 Dodecyl 4.5 Example 3:methacrylate Synthesis CP-4  M-3 54.7 AA 5.3 — — Example 4: SynthesisCP-5  M-3 53.9 AA 6.1 — — Example 5: Synthesis CP-6  M-3 45.1 MAA 14.9 —— Example 6: Synthesis CP-7  M-5 36.5 AA 21.9 Styrene 1.7 Example 7:Synthesis CP-8  M-3 35.0 AA 25.0 — — Example 8: Synthesis CP-9  M-3 47.6AA 12.4 — — Example 9: Synthesis CP-10 M-8, M-9 49.7 AA 10.3 — — Example10: Synthesis CP-11 M-3 40.4 MAA 19.6 — — Example 11: Synthesis CP-12M-5 47.9 AA 12.1 — — Example 12: Synthesis CP-13 M-5 47.3 AA 12.7 — —Example 13: Synthesis CP-14 M-3 36.3 AA 23.7 — — Example 14: SynthesisCP-15 M-3 45.9 AA 12.0 Styrene 2.2 Example 15: Synthesis CP-16 M-5 44.2AA 8.4 Dodecyl 7.4 Example 16: methacrylate Synthesis CP-17 M-8, M-952.2 AA 7.8 — — Example 17: Synthesis CP-18 M-3 44.4 MAA 15.6 — —Example 18: Chain Polym- Polym- transfer erization erization adjustingtem- Chemical Initiator agent perature formula 2 AIBN Thioglyceroldegrees Ratio Produced polymer Part Part C. Percent Mw Part Synthesis2.3 0.2 75 79.3 22000 58.5 Example 1: Synthesis 2.3 0.1 75 75.7 2410057.4 Example 2: Synthesis 2.3 0.2 75 71.3 21000 58.8 Example 3:Synthesis 2.3 — 75 91.1 26600 58.7 Example 4: Synthesis 1.5 — 70 89.843700 58.2 Example 5: Synthesis 2.3 0.3 75 75.1 19000 59.3 Example 6:Synthesis 2.3 0.3 75 60.8 19800 57.5 Example 7: Synthesis 2.3 0.3 7558.3 18500 58.4 Example 8: Synthesis 0.8 — 70 79.3 54000 58.8 Example 9:Synthesis 1.4 — 70 82.8 48500 59.6 Example 10: Synthesis 1.5 — 75 67.339000 59.1 Example 11: Synthesis 3.9 0.5 75 79.8 16300 57.7 Example 12:Synthesis 4.3 0.8 75 78.8 5300 55.7 Example 13: Synthesis 5.0 1.2 7560.6 4400 56.3 Example 14: Synthesis 2.3 0.1 75 76.5 25300 58.3 Example15: Synthesis 3.5 0.5 75 73.7 12000 57.7 Example 16: Synthesis 3.5 0.875 87.1 8100 55.9 Example 17: Synthesis 1.9 — 75 74.1 36400 59.9 Example18:

TABLE 2 Pure Kind of pigment water + Pigment Pigment Pigment Pigment pHpH Carbon Blue Red Yellow dispersion Copolymer regulator regulator Black15:3 122 74 PD-1  CP-1  4.0 TEAOH 80.0 16.0 PD-2  CP-2  4.0 TEAOH 80.016.0 PD-3  CP-3  4.0 TEAOH 80.0 16.0 PD-4  CP-4  4.0 TEAOH 80.0 16.0PD-5  CP-5  4.0 TEAOH 80.0 16.0 PD-6  CP-6  4.0 NaOH 80.0 16.0 PD-7 CP-7  4.0 NaOH 80.0 16.0 PD-8  CP-8  4.0 TEAOH 80.0 16.0 PD-9  CP-9  4.0TEAOH 80.0 16.0 PD-10 CP-10 4.0 TEAOH 80.0 16.0 PD-11 CP-11 4.0 DEA 80.016.0 PD-12 CP-12 4.0 TEAOH 80.0 16.0 PD-13 CP-13 4.0 TEAOH 80.0 16.0PD-14 CP-14 4.0 TEAOH 80.0 16.0 PD-15 CP-15 4.0 TEAOH 80.0 16.0 PD-16CP-16 4.0 TEAOH 80.0 16.0 PD-17 CP-17 4.0 NaOH 80.0 16.0 PD-18 CP-18 4.0DEA 80.0 16.0 PD-19 CP-1  1.6 TEAOH 82.4 16.0 PD-20 CP-1  10.0 TEAOH74.0 16.0 PD-21 CP-1  6.0 TEAOH 74.0 20.0 PD-22 CP-1  6.0 TEAOH 74.020.0 PD-23 CP-1  6.0 TEAOH 74.0 20.0

TABLE 3 Ink name Pigment dispersion Example 1 GJ-1  PD-1  40.0 Example 2GJ-2  PD-2  40.0 Example 3 GJ-3  PD-3  40.0 Example 4 GJ-4  PD-4  40.0Example 5 GJ-5  PD-5  40.0 Example 6 GJ-6  PD-6  40.0 Example 7 GJ-7 PD-7  40.0 Example 8 GJ-8  PD-8  40.0 Example 9 GJ-9  PD-9  40.0 Example10 GJ-10 PD-10 40.0 Example 11 GJ-11 PD-11 40.0 Example 12 GJ-12 PD-1240.0 Example 13 GJ-13 PD-13 40.0 Example 14 GJ-14 PD-14 40.0 Example 15GJ-15 PD-15 40.0 Example 16 GJ-16 PD-16 40.0 Example 17 GJ-17 PD-17 40.0Example 18 GJ-18 PD-18 40.0 Example 19 GJ-19 PD-19 40.0 Example 20 GJ-20PD-20 40.0 Example 21 GJ-21 PD-21 40.0 Example 22 GJ-22 PD-22 40.0Example 23 GJ-23 PD-23 40.0 Water-Soluble Solvent Ethylene 1,3-3-methoxy- 3-ethyl-3- glycol 2,2,4- butane N,N-dimethyl hydroxymethylmonobutyl 2- 2-ethyl-1,3- trimethyl-1,3- Glycerin diol propionamideoxetane ether pyrroridone hexanediol pentanediol Example 1 10.0 20.0 1.01.0 Example 2 10.0 10.0 20.0 1.0 1.0 Example 3 5.0 30.0 1.0 1.0 Example4 10.0 25.0 1.0 Example 5 5.0 10.0 15.0 10.0 1.0 Example 6 10.0 10.010.0 1.0 Example 7 10.0 20.0 1.0 1.0 Example 8 10.0 10.0 10.0 1.0 1.0Example 9 5.0 40.0 1.0 1.0 Example 10 5.0 30.0 1.0 Example 11 10.0 30.01.0 1.0 Example 12 10.0 10.0 5.0 10.0 Example 13 5.0 20.0 10.0 1.0 1.0Example 14 10.0 20.0 1.0 1.0 Example 15 10.0 10.0 10.0 1.0 Example 165.0 10.0 15.0 1.0 Example 17 10.0 10.0 10.0 1.0 1.0 Example 18 10.0 20.01.0 1.0 Example 19 10.0 20.0 20.0 1.0 1.0 Example 20 10.0 10.0 5.0 5.01.0 Example 21 30.0 1.0 1.0 Example 22 10.0 20.0 10.0 1.0 1.0 Example 2310.0 20.0 1.0 1.0 Surfactant UNIDYNE ™ DSN-403N Pure water Example 1 1.027.0 Example 2 1.0 17.0 Example 3 1.0 22.0 Example 4 2.0 22.0 Example 51.0 18.0 Example 6 1.0 28.0 Example 7 2.0 26.0 Example 8 1.0 27.0Example 9 1.0 12.0 Example 10 1.0 23.0 Example 11 2.0 16.0 Example 121.0 24.0 Example 13 1.0 22.0 Example 14 1.0 27.0 Example 15 2.0 27.0Example 16 1.0 28.0 Example 17 1.0 27.0 Example 18 1.0 27.0 Example 191.0 7.0 Example 20 2.0 27.0 Example 21 1.0 27.0 Example 22 1.0 17.0Example 23 1.0 27.0

TABLE 4 Pigment Plain Plain dispersion Ink paper 1 paper 2 Storagestorage Image Image stability stability Density Density Example 1 G G GG Example 2 G G G G Example 3 G A G A Example 4 A A A A Example 5 G A GA Example 6 G G G G Example 7 G A G A Example 8 A A A A Example 9 A A AA Example 10 G A G A Example 11 G A G A Example 12 G G G G Example 13 GA G A Example 14 A M A M Example 15 G G G G Example 16 A A A A Example17 G A G A Example 18 G A G A Example 19 G A G A Example 20 G A G AExample 21 G G G G Example 22 A A G G Example 23 G G G G Comparative P PM P Example 1 Comparative P P P P Example 2 Comparative P P P P Example3 Comparative P P P P Example 4 Comparative P P M P Example 5Comparative M P M M Example 6

As seen in the results, the pigment dispersions prepared by using thecopolymers having a naphtyl group at their distal end of the side chainof Examples 1 to 23 related to the present disclosure have betterstorage stability than the pigment dispersions prepared by using thecopolymers having no naphtyl group at their distal end of the side chainof Comparative Examples 1 to 5. The detailed mechanism is not clear butcan be inferred as follows.

To achieve good pigment dispersion and dispersion stability, copolymerresins are firmly adsorbed and re-agglomeration of pigment particles isprevented due to steric barrier of the resins between pigment particlesat the same time.

The copolymer related to the present disclosure is inferred to haveexcellent property with regard to the above-mentioned. In aqueous ink,adsorption of a copolymer resin and a pigment is caused by mutualattraction due to hydrophobic mutual interaction and aromatic stackingmutual interaction (π-π mutual interaction). The copolymer related tothe present disclosure includes the structure unit represented by theChemical formula 1 serving as hydrophobic part and the structure unitincluding an anionic group serving as hydrophilic part. Due to stronghydrophilicity by the anionic part, it is possible to include thestructure unit represented by the Chemical formula 1 in a highconcentration while securing aqueous property so that great hydrophobicmutual interaction is demonstrated. In addition, the hydrophobic parthas a naphytyl group so that a great π-π mutual interaction is obtained.Due to these combination, the copolymer resin is strongly adsorbed tothe pigment. Moreover, the copolymer resin related to the presentdisclosure is inferred that, due to its structural feature, it ispossible to continue holding repulsion between pigment particles due tosteric barrier and electrostatic repulsion.

In addition, if a structure unit similar to the structure unitrepresented by the Chemical formula 1 in terms of having a naphtyl groupat its distal end of the side chain but different therefrom is used,storage stability of ink is not sufficient so that securing stablequality for an extended period of time is not easy (Refer to ComparativeExample 6).

Moreover, image forming, recording, printing, modeling, etc. in thepresent disclosure represent the same meaning.

Having now fully described embodiments of the present invention, it willbe apparent to one of ordinary skill in the art that many changes andmodifications can be made thereto without departing from the spirit andscope of embodiments of the invention as set forth herein.

What is claimed is:
 1. Ink comprising: water; a coloring material; and acopolymer including a first structure unit represented by the followingChemical formula 1 and a second structure unit including an anionicgroup,

where R represents a hydrogen atom or a methyl group, X represents analkylene group having 2-4 carbon atoms, and Y represents a substitutedor non-substituted straight-chain alkylene group having 5 to 7 carbonatoms.
 2. The ink according to claim 1, wherein the second structureunit includes a carboxylic group.
 3. The ink according to claim 1,wherein a proportion of the first structure unit in the copolymer is 75percent by mass-90 percent by mass.
 4. The ink according to claim 1,wherein a mass average molecular weight of the copolymer is15,000-40,000.
 5. A method of manufacturing ink including water, acoloring material, and a copolymer, comprising: synthesizing thecopolymer by radical polymerization of a monomer mixture including amonomer represented by the following Chemical formula 2 and a monomerincluding an anionic group,

where R represents a hydrogen atom or a methyl group, X represents analkylene group having 2-4 carbon atoms, and Y represents a substitutedor non-substituted straight-chain alkylene group having 5 to 7 carbonatoms; and mixing the copolymer, the coloring material, and the water.6. An ink cartridge comprising: the ink of claim 1; and a container toaccommodate the ink of claim 1.